Variable venturi carburetor



Dec. 18, 1962 J. H. MacNEILL VARIABLE VENTURI CARBURETOR 2 Sheets-Sheet 1 Filed Aug. 50, 1960 FIG.

llllllll II IIIII Ill ll I I I l ll ll lilllll ll INVENTOR. John H. Mac Neill 1 ATTORNEYS- Dec. 18, 1962 J. H MaONElLL VARIABLE VENTURI CARBURETOR 2 Sheets-Sheet 2 Filed Aug. 30, 1960 FIG. 3.

INVENIOR. John H.MacNe/ll BY f A TTORNEYS United States Patent 1 3,069,146 VARIABLE VENTURI CARBURETOR John H. MacNeill, Melbourne, Fla, assignor to Soroban Engineering, Inc., Melbourne, Fla, a corporation of Florida Filed Aug. 30, 196i), Ser. No. 52,990 7 Claims. (Cl. 261-44) The present invention relates to carburetors for internal combustion engines and more particularly to variable venturi carburetors.

The advantages obtainable with the variable venturi carburetor as opposed to the constant diameter carburetor are well known and relate to the ability of the former device to maintain a constant fuel-air ratio over large changes in air flow with a relatively simple apparatus. In the conventional constant diameter venturi carburetor, an attempt is made to maintain proper fuelair ratios with changes in the flow rates by varying the size of the fuel metering orifices as a function of the position of the butterfly valve and/or the utilization of airbl'eed orifices. However, such an apparatus maintains a proper fuel-air ratio over only a relatively limited range of air flow which is insuflicient to handle the present day high horsepower engines. In consequence, resort has been had to multiple barrel carburetors having progressively operated throttle linkages. Each of the barrels of the carburetor is capable of maintaining a constant fuel-air ratio over a limited change in air flow and progressively operating throttle linkages are provided to sequentially and successively actuate the throttle or butterfly Valves associated with each of the barrels of the carburetor. Therefore each barrel is subjected to only a limited change in air volume while the total change in volume of air flow is the sum of the change permitted by each barrel. The total change in air flow in such an arrangement may vary from the idling air flow for one of the barrels to the full flow of all barrels when the accelerator has been fully depressed.

The multiple barrel carburetor as described above is a complex mechanism and the problem of providing a constant fuel-air ratio over large changes in flow Volumes has been solved more simply by utilizing the variable venturi carburetor. In the variable venturi carburetor the area of the throat of the venturi is varied as a function of the desired air flow rate. There are at present two major classes of variable venturi carburetors; those in which the venturi segments are operated directly by the throttle linkage and, in a second class, those which employ a butterfly valve and utilize the pressure between the butterfly valve and the variable venturi segments to control the position of the latter elements. Although both of these apparatus solve, to a greater or lesser extent, the problem relating to a constant fuel-air ratio over the large changes in quantity of air flow, both of these devices suifer from disadvantages which are eliminated by the apparatus of the present invention.

In variable venturi carburetors wherein the throttle linkage directly controls the venturi segments when it is wished to accelerate the vehicle rapidly, the accelerator is rapidly depressed, and the cross-sectional area of the throat of the venturi is suddenly increased many fold. Since the engine does not accelerate instantaneously, the volume of air flowing through the venturi of the carburetor does not materially increase at the instant the venturi cross-sectional area is increased. Therefore, a condition exists in which the area of the throat has been suddenly increased while the air flow remains approximately constant. This causes a sudden decrease in pressure drop across and a rise in pressure in the venturi. The pressure differential across the fuel valve decreases and the amount of fuel extracted is decreased. Further, the atomization of the fuel becomes incomplete due to the relatively low velocity of the air. Consequently, the

3,069,146 Patented Dec. 18, 1962 engine tends to become starved for fuel and this coupled with incomplete combustion of the available fuel, which results from poor mixture of the air and fuel, may either cause the engine to become starved for fuel and to die completely or at least experience a sudden, although temporary reduction in motor torque.

The variable venturi carburetor employing a butterfly valve overcomes the problems of the variable venturi carburetor described above, since it tends to be self regulating. In this latter device, the venturi segments are positioned as a function of the pressure between the venturi and the butterfly valve. At the instant of opening of the butterfly valve, the pressure across this valve decreases thereby decreasing the pressure immediately below the venturi. This decrease in pressure opens the venturi throat and in so doing increases the pressure below the venturi which limits the degree to which the venturi throat may be opened. Thus, the system has a servo loop which is self-regulating since the venturi diameter and the pressure below the venturi are interdependent parameters which establish equilibrium conditions at a constant pressure below the venturi. Since these two parameters are interacting, the only independent parameter in the system is the total air flow and consequently the venturi cross-sectional area is primarily a function of this latter quantity. Thus, the situation does not arise, as in the previously described variable venturi carburetor, wherein there is an excessive loss of pressure across the venturi which reduces the fuel intake. In fact, in the arrangement under discussion, opening of the butterfly "alve causes an immediate increase in the fuel supplied since the pressure across the venturi and therefore, across the fuel valve increases. The increase in fuel increases the speed of the motor and increases the rate of air flow which further widens the venturi throat. Relatively constant air velocity across the fuel jet maintains the same degree of fuel atomization at all flow rates.

In order to maintain the fuel-air ratio constant, the area of the fuel valve opening is regulated as a function of the area or Width of the venturi throat, so that as the area of the venturi throat is increased as a function of air flow, the fuel valve is opened also in direct proportion to the air flow and the ratio remains approximately constant, or can be controlled to match any desired function of fuel-air ratio versus flow rate. (See L. C. Lichty, Internal Combustion Engines, 5th ed. chapter IX.)

Although the variable venturi carburetor employing a butterfly valve has advantages over the carburetor wherein the venturi area is controlled directly by the throttle linkage, difficulties arise as a result of the use of the butterfly valve. Specifically, the butterfly valve introduces an asymmetry into the flow of the fuel and air mixture as it comes out of the venturi and therefore affects the distribution of fuel and air in the cylinder of the engine. Another difliculty with such apparatus is that the butterfly valve takes up a relatively large amount of space particularly in a vertical carburetor. This is undesirable in the modern automobile with its low hood lines since relatively little vertical space is provided under the hood. In order to overcome this difliculty, in some automobiles, the butterfly valve has been placed to project partly into the manifold thereby partially reducing the problem of vertical height. However, the projection of the butterfly valve partially into the manifold further increases the problems resulting from the asymmetry of the flow of the fuel-air mixture caused by the butterfly valve.

In accordance with the present invention, there is provided a variable venturi carburetor which neither em-' ploys a butterfly valve nor directly operates on the variable venturi segments. Instead the throttle linkage controls a small valve externally of the carburetor which valve develops a pressure in a suitable chamber which is variable over a range between atmospheric pressure and the pressure existing in the carburetor below the venturi region, the actual pressure at any instant being a function of the position of the valve. The positioning of the valve and the pressure in the carburetor determine the pressure in the chamber and this pressure is utilized to position variable venturi segments to control the venturi opening. Once the throttle control valve has been adjusted and even during its adjustment, the variable venturi segments are regulated at least partially in the latter case, as a function of the pressure in the carburetor below the venturi segments and as in the prior art variable venturi carburetors utilizing butterfly valves, a servo loop is established that prevents a too rapid opening of the venturi even though the butterfly valve has been eliminated.

The same apparatus which is employed to vary the position of the variable venturi segments of the apparatus of the present invention is also utilized to position the needle valve in the fuel control line and therefore, the amount of fuel fed through the carburetor is a function of the position of the variable venturi segments and therefore, of the total air flow through the apparatus. It is seen that this arrangement can maintain a proper fuelair ratio and that due to the utilization of the variable venturi segments very large changes in air flow are obtainable. In consequence, the apparatus of the present invention provides a controllable fuel-air ratio variable venturi carburetor in which the butterfly valve has been eliminated but in which the advantages of this type of carburetor as opposed to the variable venturi carburetor in which the variable venturi segments are operated directly from the throttle control valve, are retained.

It is an object of the present invention to provide a variable venturi carburetor in which the variable venturi segments are positioned in accordance with a pressure that is intermediate the atmospheric pressure and of the pressure in the carburetor below the venturi; which ratio is varied in accordance with the position of a throttle operated valve.

It is another object of the present invention to provide a variable venturi carburetor in which the conventional butterfly valve is eliminated and in which variable venturi segments of the carburetor are not operated directly by a throttle linkage.

It is another object of the present invention to provide a variable venturi carburetor in which the position of the variable venturi segments and the fuel control or needle valve of the carburetor are both functions of a pressure that is proportional to a ratio of the atmospheric pressure and of the pressure in the carburetor below the venturi; which ratio is varied in accordance with the position of a throttle operated valve.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a top view of the carburetor illustrated in FIGURE 2;

FIGURE 2 is a vertical partial cross section of the carburetor of the present invention;

FIGURE 3 is a vertical view in section of a modification of the apparatus illustrated in FIGURE 2; and

FIGURE 4 is a top view in partial section of the device of FIGURE 3.

Referring specifically to FIGURES l and 2 of the accompanying drawings, the carburetor has a main hollow body 1 which is generally rectangular in its horizontal cross section and includes sidewalls 4, 5, 6 and 7. The body 1 terminates at its lower end, as viewed in FIGURE 1, in a generally elliptical flange 2 which is adapted to contact an intake manifold of the internal combustion engine and may be bolted thereto by passing bolts through apertures 3 provided in the flange 2. The opposed side walls and 7 are provided with apertures 8 and 9, re-

spectively, extending substantially across the width of the walls. The apertures 8 and 9 are generally rectangular in shape and have disposed therein variable venturi segments 11 and 12. In a vertical plane parallel to the plane of FIGURE 2, the segments 11 and 12 are generally the shape of one-half of an inverted teardrop and in the other vertical plane are generally rectangular. The variable venturi segment 11 is secured to and rotatable with a shaft 13 which extends across the lower region of the aperture 8 and is pivoted in the body 1 at the junctions of the end walls 4 and 6 with the side wall 5. A shaft 14 extends through the lower region of the aperture 9 in the side wall 7 and is pivotally received in the body 1 at the junctions of the side walls 4- and 6 with the side wall 7. The variable venturi segment 12 is secured to the shaft 14 for rotation therewith. The segments 11 and 12 are in sealing relationship with the walls 5 and 7 respectively so as to prevent excessive leakage between the segments .11 and 12 and the walls 5 and 7 respectively. Alternatively, the walls 5 and 7 may bow outwardly in the region of the segments 11 and 12 and form a seal around the apertures in the wall in which the segments are disposed; this may be necessary to maintain proper force balance in a preferred form of the invention.

The shafts 13 and 14- extend outwardly from the body of the carburetor 1 and the shaft 13 has a generally downwardly depending arm 16 secured thereto. The shaft 14 externally of the carburetor has a generally upwardly extending arm 17 secured thereto and the ends of the arms 16 and 17 remote from the shaft 13 and 14 respectively are pivotally interconnected by a link 18. In consequence when the shaft 14 is rotated clockwise, to rotate the variable venturi segment 12 towards the center of the. carburetor chamber, the arm 17 is rotated clockwise and causes the link 18 to translate towards the right. This causes the arm 16 to rotate counterclockwise and rotate the shaft 13 in the same direction. The segment 11 also rotates counterclockwise towards the center of the carburetor body. Therefore the segments 11 and 12 are constrained to rotate in opposite directions about the axis of their respective shafts and to open or close the passage through the carburetor body as dictated by rotation of the shaft 14.

Rotation of the shaft 14 is controlled by an arm 19 secured to the shaft 14. The arm 19 is illustrated in FIG- URE 1 as generally horizontal and is connected at one end to a vertical link 21 extending upwardly from a piston 22 of a piston and cylinder mechanism 23. The piston 22 is biased upwardly by a compression spring 24 extending between a bottom wall 26 of the mechanism 23 and the piston 22. Air is admitted to the mechanism 23 under the piston 22 through a pipe 27 communicating with the interior of a valve body 28. The mechanism 23 and valve body 28 are not in the same vertical plane and as illustrated in FIGURE 2 the pipe 27 is an L-shaped member with a short leg extending vertically up from the valve body 28 and a long leg extending horizontally into the side of the body of the dashpot 23. The interior of the valve body 28 is connected to atmospheric pressure via a pipe 29 and is connected to the interior of the carburetor below the variable venturi segments 11 and 12 via a pipe 31. The valve body 28 is provided with a semi-circular valve 32 carried on a shaft 33. The shaft 33 is rotated by a throttle linkage member 34 which is rotatable about the axis of the shaft 33 as its center.

The valve 32 controls the pressure within the mechanism 33 by controlling the degree of opening of the pipe 27 to atmospheric pressure or the pressure within the carburetor belowthe variable venturi segments 11 and 12.

"If the valve 32 is in the position illustrated, the pipe 27 is connected to atmospheric pressure whereas, if the valve is rotated into the dotted line position, the pipe 27 is connected to the internal pressure of the carburetor. Intermediate positions of the valve 32 cause the pressure with the pipe 27 to assume a value intermediate the two extremes mentioned above with the actual pressure being determined by the degree of opening between the pipe 27, the pipes 29 and 31 and the pressure within the carburetor. The top of the mechanism 23 is exposed to atmospheric pressure and therefore the position of the piston 2 is a function of the pressure differential between atmospheric pressure and the pressure in the pipe 27. Specifically, if the pipe 27 is vented to the atmosphere via the pipe 29, there is no pressure differential across the piston 22 and the position of the piston 22 becomes a function of the spring 24. Since the. spring 24 is a compression spring, it expands fully and the venturi segments 11 and 12 are rotated to their fully closed position. If, on the other hand, the valve 32 is positioned to block completely the pipe 29 and connect the pipe 27 to the pipe 31, the piston 22 assumes a position as determined by the pressure in the carburetor below the segments 11 and 12. The differential between atmospheric pressure and the pressure within the carburetor causes the piston 22 to be depressed and the venturi segments 11 and 12 are rotated in a direction to open the passage through the carburetor.

The apparatus of the present invention is also provided with a fuel inlet apparatus comprising a horizontal rod 36 extending between and secured in the walls and 7 of the carburetor. The rod 36 is drilled to provide a passage to approximately the center of the body and is connected to the fuel float bowl or pressure regulating diaphragm so as to provide a fuel input to the carburetor.

The rod 36 has a downwardly extending tube 38 disposed centrally of the carburetor body 1. The tube 38 extends downwardly from the rod 36 into the region of the variable venturi segments 11 and 12. The segments are provided with arcuate depressions 48 and 49 respectively of such a depth that the venturi segments may be closed completely with the tube 38 received in the depressions 43 and 49. Actually the depth and width of the depressions 48 and 49 are greater than the corresponding radius of the tube 38 so that a small air passage is provided around the tube 38 and through the segments 11 and 12. This arrangement serves to provide for flow of air to the motor during idling conditions when segments 11 and 12 are in line contact throughout their length except in the region of the depressions 48 and 49.

The interior of the tube 38 is in communication with 1 the passage 37 in the rod 36. A needle valve 39' is disposed within the tube 33 and extends through an aperture in the top of the rod 36. The needle valve 39 is tapered at its lower extremities and is adapted to extend through an aperture 41 at the bottom of the tube 38. The upper end of the needle valve 39 is connected to a generally horizontal arm 42 which passes through an aperture 43 in the wall 7 of the carburetor body and is pivoted at 44 externally of the wall 7. The arm 42 is pivotally secured to a link 45 having a vertical leg 46 and a horizontal leg 47. The horizontal leg is pivotally secured to the horizontal arm 19 and therefore, if the arm 19 is rotated about the axis of the shaft 14, the leg 46 of the link 45 translates vertically. This imparts pivotal movement to the arm 42 about its pivot point 44 imparting vertical translating motion to the needle valve 39.

In operation, with the valve 32 in the full line position illustrated in FIGURE 2, atmospheric pressure is developed in the passage 27 and the piston 22 assumes its upwardmost position. With the piston in such position the segments 11 and 12 are in contact with one another and the only passage for air through the carburetor is through the regions of the depressions 48 and 49 in segments 11 and 12 respectively not occupied by the tube 38. Thus, idling conditions are established. Upon rotation of valve 32 by means of the throttle linkage member 34, the pressure at the entrance to the pipe 27 becomes a function of the position of the valve 32. A pressure less than atmospheric is introduced under the piston 22 resulting in a net downward force on the piston. Downward movement of the piston 22 opens the venturi passage through the carburetor and concurrently lifts the needle valve 39 so that a desired value of the fuelair ratio is established. The final position of the various elements is determined by the position of the valve 32 since it is the position of this valve which determines the pressure under the piston 22. The system always assumes the same final position for a given opening of valve 32 and the same engine speed or load since there is only one position for all of the elements at which the air flow through the carburetor establishes a pressure below piston 22 such that the differential in pressure across the piston balances the force of the spring 24. As previously indicated, the system is in etfect a closed loop servo. If the elements tend for any reason to move away from their equilibrium position a corrective action takes place immediately. For. instance, if the segments 11 and 12 tend to rotate to open the venturi passage, the pressure below the segments increases and the pressure across the piston 22 decreases. The piston moves upwardly under the force of the spring and closes the passage through the carburetor until the forces in the system are again in balance. Since the apparatus is, in etfect, a closed loop servo system damping may be desirable and can be provided by a dashpot suitably connected to the carburetor linkage.

It will be seen from the above that the apparatus illustrated in FIGURES 1 and 2 neither employs a butterfly valve nor direct connection between the throttle linkage and the venturi segments. The advantages, with respect to sudden acceleration, of the variable venturi carburetor employing a butterfly valve are obtained but the disadvantages incident to the use of a butterfly valve are not encountered. It is seen further, that starving of the engine due to sudden opening of the variable venturi cannot occur since, when the valve 32 is rotated, the movement of the venturi segments is under control of the pressure below the venturi. Therefore, if the apparatus tends to produce a sudden drop in pressure in this portion of the carburetor, the variable venturi segments 11 and 12 are rotated only a very small amount and in consequence, starving of the engine for fuel which results from a sudden reduction in pressure across the fuel supply valve is not encountered.

In theembodiment of the invention illustrated in FIG- URES 1 and 2, a piston and a cylinder mechanism 23 is employed to sense the pressure in the pipe 27 and to translate this pressure into a mechanical movement that is subsequently employed to control the needle valve 39 and the variable venturi segments 11 and 12. In a modification of the invention, illustrated in FIGURES 3 and 4 of the accompanying drawings, the pressure developed in the pipe 27 is utilized directly to control the variable venturi segments and the piston and cylinder mechanism 23 is eliminated.

Referring now specifically to FIGURES 3 and 4, the walls 5 and 7 are provided with outwardly extending, generally rectangular enclosures 51 and 52 respectively which seal the region behind the variable venturi segments. The variable segments 11 and 12 are biased inwardly towards the center of the carburetor by springs 53 and 54, respectively, and the pipe 27 is in direct communication with the generally rectangular enclosures 51 and- 52, interconnected by a pipe 55. In consequence, the variable pressure developed in the pipe 27 is also developed behind the variableventuri segments 11 and 12 which, as previously indicated, are arranged in sealing relationship with the walls 5 and '7 respectively. There fore, the regions defined by the rectangular extensions 51 and 52 and the segments 11 and 12 are variable pressure regions and the positions of the segments 11 and 12 are a function of the pressure in the pipe 27 and the pressure below the venturi. The compression springs 53 and '54 disposed in the chamber 51 and 52 behind the segments 11 and 12, respectively, tend to rotate the segments toward the center of the carburetor body 1. In

this embodiment of the invention, atmospheric pressure is exerted on the upper portions of the segments 11 and 12 and the force developed by the difference in pressure across the segments tends to press the segments 11 and 12 outwardly into the rectangular enclosures 51 and 52 against the force of the springs 53 and 54. If the pipe 27 is coupled to the pipe 31, the force of the springs 53 and 54 minus the ditferential in pressure across the venturi of the carburetor, acting on the upper portion of the segments, opens the segments to the extent necessary to fulfill the air requirements of the engine. If the pipe 27 is in communication with pipe 29, the same pressure is developed on both sides of the upper portion of the segments and under the force of the springs and the pressure ditference across the lower portions of the segments, the segments are moved to close the venturi passage.

In this embodiment of the invention, the linkage comprising members 16, 17 and 13 is retained and the portion of the arm 19 between shaft 14 and the horizontal leg 47 of the link 45 is also retained. Therefore, the position of the needle valve 39 is still controlled in accordance with the position of the variable venturi segments 11 and 12 and the only difference between the embodiments of FEGURES l and 2 on the one hand and of FIGURES 3 and 4 on the other is the elimination of the piston and cylinder mechanism 23.

The apparatus of the invention as illustrated in FIG- URES 3 and 4 may be altered by bleeding the region defined by Walls 51 and 52 to the atmosphere and con necting the valve 28 between the pipe 31 and the pipe 55. Alternatively the pipe 55 may be connected by a small passage or bleed to the pipe 31 and the valve 28 connected between the pipe '55 and atmospheric pressure. In both instances the final pressure in the regions defined by S1 and 52 have a pressure established therein which is variable between atmospheric pressure and the pressure below segments 11 and 1.2 as a function of the position of valve 28.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What 1 claim is:

1. A variable venturi carburetor comprising a carburetor having an airflow passage therethrough, a movable ven turi means disposed in said airflow passage, means for mounting said venturi means for movement into and out of said airflow passage so as to vary the flow area past said venturi means, a chamber, a first flow path con meeting with said airflow passage on the downstream side of said venturi means, a second flow path connecting with atmospheric pressure, and throttle control means for selectively connecting said chamber only with said first flow path, only with said second flow path and in variable proportions to both of said flow paths to establish a pressure in said chamber which is variable between atmospheric pressure and the pressure in the downstream side of said venturi means and means for moving said venturi means as a function of the pressure in said chamher 2. A variable venturi carburetor comprising a carburctor body having a passage therethrough, movable venturi means disposed in said passage, means for mounting said venturi means for movement into and out of said passage so as to vary the flow area past said venturi means, a chamber control means for producing a pressure in said chamber variable substantially over the entire range between atmospheric pressure and the pressure in the carburetor passage on the downstream side of said venturi means, said control means including a throttle control means external to said passage for selectively and variably connecting said chamber to said atmospheric pressure and said pressure in said carburetor to vary said pressure in said chamber, and means for moving said venturi means as a function of said pressure, a fuel supply means capable of supplying variable quantities of fuel to said carburetor passage in the region of said venturi means, and means for varying the quantity of fuel supplied by said fuel supply means as a function of the pressure in said chamber.

3. A variable venturi carburetor comprising a carburetor body having a passage therethrough, movable venturi means disposed in said passage, means for mounting said venturi means for movement into and out of said passage so as to vary the flow area past said venturi means, a chamber, a first flow path connecting with said airflow passage on the downstream side of said venturi, a second flow path connecting with atmospheric pressure, a valve means for selectively and variably connecting said chamber to said flow paths to vary the pressure in said chamber, throttle control means for operating said valve, and means for moving said venturi means as a function of the pressure in said chamber.

4. A variable venturi carburetor comprising a carburetor body having a passage therethrough, movable venturi means disposed in said passage, means for mounting said venturi means for movement into and out of said passage so as to vary the flow area past said venturi means, a chamber, a first fiow path connected to atmospheric pressure, a second flow path connected to a region in said passage below said venturi means, a valve continuously movable between two positions in which said chamber is coupled respectively to one and the other of said flow paths to vary the pressure in said chamber, a throttle control means for varying the position of said valve so as to vary said pressure, means for moving said venturi means as a function of the pressure in said chamber such that the areas of flow in the region of said venturi segment means is decreased with an increase in said pressure, a fuel supply means capable of supplying variable quantities of fuel to said carburetor passage in the region of said venturi means, and means for varying the quantity of fuel supplied by said fuel supply means as a function of said pressure such that the quantity of fuel supplied is decreased as said pressure is increased.

5. The combination according to claim 4 wherein said chamber comprises a sealed region defined by said venturi means and outer walls of said carburetor body.

6. The combination according to claim 4 wherein said chamber comprises a cylinder, and a piston and a spring for biasing said piston to a predetermined position therein, and wherein said means for moving comprises a mechanical linkage between said venturi means and said piston.

7. The combination according to claim 6 wherein said means for varying the quantity of fuel comprises a linkage between said piston and said fuel supply means.

References Cited in the file of this patent UNITED STATES PATENTS 

